There are a variety of security systems which use electronically encoded devices in operation. These systems generally use some type of an identification or security code which is stored in a locking device to be unlocked with a key which contains a corresponding identification or security code. These types of devices, such as those disclosed in U.S. Pat. Nos. 5,140,317 (the "'317 patent") issued to Hyatt Jr., et al. and 4,250,533 (the "'533 patent") issued to Nelson, provide for transfer and comparison of identification codes between the key and lock or bolt device. If the codes being compared are identical, then the security device changes states from locked to unlocked or vice versa. For these types of security devices, there are various ways that power and/or data can be transferred between a lock and key, such as by using a light emitting diode (LED) and photosensor or by using traditional contacts between the lock and key device. With the use of contacts to transmit power and data, there is a potential that the contact points will become damaged or worn such that operation of the device becomes difficult or impossible. In devices that use an LED and photosensor to transfer data, an additional power source is typically needed, as disclosed in the '317 patent, and there is a potential for erroneous data transfer if the photosensor or LED become mis-aligned or damaged.
There are also other problems that have been experienced with prior lock and key devices which use electronically encoded identification codes to operate. For instance, some electronically encoded lock and key devices do not have a self-contained power supply. This creates the need for an additional item (i.e., a separate power supply) to operate the system. Furthermore, many of these lock and key systems have only "one-way" communication between the key and lock. Therefore, there are several desirable features which are not available in some prior security lock and key systems. Another problem presented in the art can be the difficulty in reprogramming a particular lock if the corresponding key is lost or misplaced. Some prior art devices, such as that disclosed in the '533 patent, use a programmable read-only memory (PROM) device to store the security or identification code in the lock device. These systems typically require removing the PROM device from the lock in order to reprogram it when a key has been lost or misplaced. This requirement introduces inefficiencies into the process of reprogramming a lock and also provides the potential for damage to the PROM device and the key or lock from which it is removed.
Thus, there is a need in the art for an electronically encoded lock and key device which can provide power and transmit data through the same medium without requiring a light source with a photosensor or other optical connections and without requiring the use of direct contacts, and which has a self-contained power source and provides for two-way communication between the lock and key devices.